The invention relates to a display device comprising an electro-optical display medium between two supporting plates, a system of pixels arranged in rows and columns, with each pixel being formed by picture electrodes arranged on the facing surfaces of the supporting plates, and a system of row and column electrodes for presenting selection and data signals, a picture electrode on one of the supporting plates being connected in an electrically conducting manner to a first non-linear asymmetric two-pole switching unit between a column electrode for data signals and the picture electrode and to a second non-linear asymmetric two-pole switching unit between the picture electrode and an electrode for a reference voltage.
A display device of this type is suitable for displaying video information and alpha-numerical information by means of passive electro-optical display media such as liquid crystals, electrophoretic suspensions and electrochromic materials.
In this Application a non-linear asymmetric two-pole switching unit is understood to mean a switching unit with a current-voltage behaviour which is asymmetrical with respect to the I axis in the current-voltage (I-V) characteristic and in which the current depends non-linearly on the applied voltage such as, for example, a diode. Such a switching unit may comprise a single switching element such as, for example, a diode or a combination of such switching elements which are arranged in series or parallel for reasons of, for example, redundancy.
A display device of the type mentioned in the opening paragraph is described in U.S. Pat. No. 5,032,831. In a device shown in this document diodes are used as switching elements. Juxtaposed columns of pixels are connected via these diodes to an electrode for a reference voltage and to drive electrodes (column electrodes) which are arranged between columns of picture electrodes. The reference voltage is used for applying, prior to selection, an auxiliary voltage across the pixel beyond or on the edge of the range of voltages to be used for picture display.
It is known that electrostatic charging may take place during the manufacture of the supporting plates on which the switching elements are provided (the active plates). A voltage difference may then occur between different column electrodes, such that there is breakdown between these column electrodes, while the switching elements or other components are damaged, and also the conducting tracks constituting the column electrodes may be damaged or may even melt.
Electrostatic breakdown may also occur between the row electrodes on the other supporting plate (the passive plate).
In a further stage of manufacture, when the active plates and passive plates have been joined and (at a still later stage) liquid crystal material or another electro-optical medium is present between the active and the passive plate, breakdown between a row and a column may also occur due to excessively high electrostatic voltages by which the switching element or a component of a pixel may be damaged. For example, degradation of the liquid crystalline material may also occur.
As the manufacture of the display device progresses, damage and consequently rejects due to electrostatic discharge will involve extremely high costs.